At the heart of performance

A study confirms that the best racehorses and the best endurance horses both have something big in common.

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New research shows that an elite endurance horse, like a top racehorse, is likely to have a larger-than-average heart.

Investigators at the University of Pennsylvania took echocardiographic measurements of the hearts of 34 Arabian horses, 23 of whom were considered elite endurance athletes based on recent competition results. They found that during both phases of the heartbeat, the left ventricle was larger in the most successful endurance horses than in average competitors.

This, explains Meg Sleeper, VMD, means that “more blood is being pumped into the body with each heartbeat,” potentially fueling a better performance. The correlation was so strong that every study horse in the elite group could be identified by this specific heart measurement alone.

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This same physiological trait has been documented in both elite Thoroughbred and Standardbred racehorses, says Sleeper. That may be due to the similar nature of their sports, she says. “I expect that in any of the sports that require significant cardiac output---for example, polo, racing, endurance or jumping---the horse with a big heart will probably have an edge, especially at the upper levels. Athleticism comes from a lot of different abilities, though. It is probably less important for a dressage horse to have exceptional cardiac output, although their balance and suppleness must be excellent for them to excel.”

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Whether these elite athletes are born with this specific trait or whether training produces it is unclear, says Sleeper. “There are definitely theories that it is genetic, and there is some evidence as well---with lots of popular legends. However, a gene in the horse has not truly been identified that is associated with a larger or athletic heart.”

Sleeper adds that designing a study to examine that would be challenging. “It is difficult to really tease it out because we know that the heart does get bigger with training, so to determine how much of the enlargement is genetic vs. environment [training] would require a big study that measured heart sizes in horses before they went into training and then again after. Part of the difficulty with assessing this in racehorse breeds is that they enter training before they are fully grown.”

Reference: “Comparison of echocardiographic measurements in elite and nonelite Arabian endurance horses,” American Journal of Veterinary Research, October 2014